OLYMPIA – Washington voters could help select the Democratic and Republican nominees for president in 2020, but only if they are willing to indicate they consider themselves a member of the party of the candidate they back.

A bill the state Senate passed Wednesday on a mostly partisan vote would give the state a presidential primary on the second Tuesday in March – rather than in late May, as required by current law – and meet national party rules for deciding how delegates are awarded.

But to cast a ballot, Washington voters, who don’t register by party, would have to say they are a Democrat or a Republican for the presidential primary. Registration rules wouldn’t change, and other primaries would remain the current top two system.

Those who consider themselves independent and refuse to pick a party for the presidential primary wouldn’t have a way to show their preference.

“This is a sort of fine line we have to walk,” said Sen. Sam Hunt, D-Olympia, the bill’s sponsor. “We can’t do everything we want.”

National party rules require that only party members get to select their nominee. In the past, that kept Democrats from using the state’s presidential primary, which sometimes has provided an “unaffiliated” option with both parties’ candidates, as an option. Washington Democrats have, instead, based their delegate selections on the caucus system while Washington Republicans have sometimes used the primary to apportion some or all of their national delegates.

Caucuses involve fewer people than primaries by preventing participation by people who have to work that day, can’t get child care to attend the meetings, are out of town or serving overseas in the military, Hunt said.

Moving the presidential primary to March means Washington voters would be involved before the nominees typically are picked and could generate more visits from candidates, supporters said.

Opponents offered an amendment to add an unaffiliated option to the 2020 presidential primary, saying that would be fairer to all voters and to taxpayers.

“It’s not the parties that are paying for this,” said Sen. Tim Sheldon, D-Potlatch.

The parties will get the names, addresses and party preferences of those who vote in the presidential primary, meaning the taxpayers are subsidizing a way for the parties to add to their fundraising lists, he said.

“I could care less about their rules. Look at who they put up for president in 2016,” he said. “I just feel the unaffiliated voters are being shafted.”

Sheldon and most Republicans voted for the amendment, which failed 18-29. The original proposal then passed 29-18 and was sent to the House.